If your wanting to get into 3D modeling and animation, but want to use an open source program, I highly suggest using Blender.
Click on Gallery to see some stuff created with it.
Blender Cookie is a great site with free tutorials. Plus, for $10 a month you get access to exclusive "Citizen" tutorials. And they are well worth the money.
Another great site for learning Blender is Blender Guru.
And for free downloadable Blender magazines with tutorials and articles check out BlenderArt Magazine.
The software has come a long way since it's original clumsy interface was updated. I dismissed the program back before version 2.5, but now I can't seem to learn all the features they keep adding to it. It opens the door to those of us on a tight budget, because of the software itself and also because of the great tutorials available.